The Ocean's Eleven star and the British lawyer visited the Chelsea Register Office where they signed a legal notice of their intent to marry.
It was posted outside of the Chelsea Town Hall, which is a legal requirement in the U.K.
The announcement also lists the location of the wedding as Italy, but a specific date was not revealed.
Reports suggest the couple, which became engaged in April (13), is planning to exchange vows next month (Sep14) at Clooney's villa in Lake Como.
Just last week (29Jul14), one of Clooney's close friends, actress Ellen Barkin, threw a bridal shower for Alamuddin at her home in New York City.